The metal and metalloid material such as arsenic, antimony and selenium is widely used as an industrial material, for example, semiconductor, but the influence on the organism by being flowed it out into an environment is concerned, since it is a harmful material for the organism.
In the past, as a method for treating these metal and metalloid, a method wherein a flocculating agent such as polychlorinated aluminum (PAC) is added into the wastewater containing an inorganic arsenic such as a harmful arsenous acid, and then the inorganic arsenic is removed by the filtration after the inorganic arsenic is aggregated, adsorbed to the flocculating agent and iron contained in a raw water and then precipitated, or a method of adsorbing an arsenic compound etc. by using an activated alumina, cerium based flocculating agent, are generally known.
On the other hand, it is known in nature that an inorganic arsenic is stored in sea food such as a seaweed, and then a part of the inorganic arsenic is converted to an organic arsenic compound such as dimethyl arsenic by the physiological response (Nonpatent literature 1). And it is generally known that these organic arsenic compound has lower toxicity than that of the inorganic arsenic for the mammal.    Nonpatent literature 1: Kaise et al., 1998, Appl Organomet. Chem., 12 137-143